This invention relates generally to semiconductor devices and more specifically to enhancing carrier concentration in a semiconductor device.
Some known semiconductor devices, such as light emitting diodes (LED), are fabricated from a group III nitride material, such as, a compositional alloy of the nitrides of Indium, Aluminum, Galium (InAlGaN). Such devices are sometimes doped with an acceptor species such as, but not limited to, magnesium (Mg) to increase free carrier concentration and therefore increase electrical conductivity.
The group III-nitride system, GaN, AlN, InN and their solid solutions, is of increasing importance in the development of optoelectronic and electronic semiconductor devices, such as light emitting diodes, lasers and heterojunction bipolar transistors. In some known semiconductor devices a p-type dopant, such as Mg, is used as a dopant for the group III-nitride materials. Mg exhibits a relatively large thermal activation energy of approximately 200 milli-electron volts (meV). Having this activation energy may result in the ionization of only a few percent of the acceptor atoms in the material at room temperature as dictated by the Fermi-Dirac statistical energy distribution. Thus, large concentrations of Mg may be required to achieve the p-type conductivity necessary for many device applications.
In some known InAlGaN devices, using Mg as a p-dopant, the InAlGaN p-type materials may require thermal activation to dissociate Mg—H complexes which form during the process of growing the p-AlInGaN material. Even after disassociation removes the hydrogen, leaving Mg dopant atoms behind, the Mg acceptor levels are typically a few hundred milli-electron volts (meV) from a valence band edge in the semiconductor device. This problem may worsen in LED's and laser diodes, as the concentration of aluminum is increased to move the emission wavelength from blue-green wavelength into an ultraviolet wavelength. Therefore, at ambient temperatures there are relatively few thermally activated holes available in the p-type AlInGaN material.